The present invention relates to a device for limiting the angular aperture in a charged particle beam system. The invention relates to a charged particle beam system for use in the production of configurations of large scale integrated circuits. The term "charged particles" used up to now designates electrons and ions. In the following description, the invention is described as using an electron beam, but this clearly is in no way limitative.
Electron beam columns have been largely developed for use in systems permitting the microproduction of large scale, integrated, semiconductor circuits. These columns are particularly useful for the inscription of selected configurations on semiconductor pellets. The function of these systems is to make a given configuration on a given area with a specified charge density and an appropriate marginal resolution. In addition, this must take place at the maximum speed.
With respect to the requirements indicated hereinbefore, various electron beam lithographic systems have been developed and used. The conventional electron beam system used for the microproduction of integrated circuits can comprise an electron beam source, condensing lenses, alignment stages, reduction lens stages, a projection lens, a deflection unit and a target area, all arranged in per se known manner.
Compared with photon lithography systems, electron beam systems have the advantage of a smaller diffraction, due to their much smaller wavelength, so that they make it possible to overcome abberations due to diffraction. However, the quality of such systems is not only dependent on the wavelength of the electrons, but also on the abberations from which they may suffer. These abberations can exist for a certain number of reasons and can in particular be mechanical abberations due to symmetry defects in the production of the mechanical parts. They may also be geometrical abberations due to the very geometry of the system, for example a spherical abberation is due to the fact that magnetic lenses are more convergent at the periphery than at their centre. This spherical abberation is proportional to the cube of the angular aperture.
Finally, in systems where the electron current is very high, there can be coulomb abberations, which increase in magnitude with the level of the electric beam current. They may consist of space charge phenomena or interactions between two electrons occurring within the beam or interference electric fields resulting from electron charges accumulated on insulants which can be, for example, condensed thin layers contaminating the conductor materials.